1. Field of the Invention
The present invention relates to a video signal processing device that digitally processes a video signal, and in particular, to a method of processing a step in a gradation region in a display image, the method comprising detecting a step of a striped pattern created in the gradation region owing to the roughness of quantization of a video signal, to eliminate the striped pattern.
2. Description of the Related Art
In the prior art, video signal processing devices (commonly referred to as graphic boards) in personal computers (referred to as PCs below) mostly realize 8-bit-equivalent gray level expression by processing a video signal of grayscale 8-bit to finally convert it into grayscale 6-bit, using the removed 2 bits to execute a dither process, and outputting the processed data to a display. Video signal processing devices in television receivers (referred to as TVs below) based on digital processing realize 10-bit-equivalent gray level expression by processing a video signal of 10-bit grayscale to finally convert it into 8-bit grayscale, using the removed 2 bits to execute a dither (commonly referred to as frame rate control [FRC]) process called a magic square algorithm, and outputting the processed data to a display.
The conventional video signal processing devices uses the dither process to reduce the roughness of quantization of the video signal. However, with these video signal processing devices, in a gradation region where the gray level varies slowly, a marked step is created in a part of the image in which quantized bits are switched. This causes a striped pattern to be displayed.
An example of a technique relating to the present invention is a method for processing a digital signal which is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2002-108298; this method involves storing correction data for luminance nonuniformity occurring in a video on a screen for each of correction points provided at fixed intervals in the screen in horizontal and vertical directions and using the correction data to perform a nonlinear interpolation operation on a video signal to add the correction data to digital data. The proposed technique relates to a process for correcting luminance nonuniformity and cannot be utilized to avoid a step created in the gradation region because of the roughness of quantization of the video signal.